1. Field of the Invention
The present invention relates to an image forming apparatus, for example, of an ink jet system, and a liquid supply apparatus having a reservoir tank to accommodate an ink liquid supplied from an ink tank, and provided with a countermeasure to remove the ink liquid remaining in a pipe to feed the ink liquid which has overflowed the reservoir tank to an overflow tank.
2. Description of the Related Art
An image forming apparatus of an ink jet system has an ink tank which accommodates an ink liquid. The ink liquid accommodated in the ink tank is supplied to an ink distribution unit through a reservoir tank. The ink liquid supplied to the ink distribution unit is supplied to a plurality of ink heads. The plurality of ink heads spout the ink liquids. An image forming medium such as a recording sheet is conveyed to a position facing the plurality of ink heads at a predetermined speed. Therefore, when the respective ink liquids spouted from the plurality of ink heads are shot on the image forming medium, an image is formed on the image forming medium.
In the image forming apparatus, for example, the ink liquid sometimes overflows the reservoir tank. In the image forming apparatus, a countermeasure for coping with an unusual operation that the ink liquid overflows the reservoir tank is taken. In one example of the countermeasure, an overflow liquid pipe is connected between the reservoir tank and an overflow tank, and the ink liquid which has overflowed the reservoir tank is fed to the overflow tank through the overflow liquid pipe.
At a usual time, when a liquid level height of the ink liquid in the reservoir tank is in the vicinity of an inflow port of the overflow liquid pipe, the ink liquid adheres or gets detached with respect to the inflow port of the overflow liquid pipe. When the ink liquid adheres or gets detached with respect to the inflow port of the overflow liquid pipe, a film of the ink liquid is formed on the inflow port by surface tension or the like. In a worst case, the film of the ink liquid formed on the inflow port sometimes solidifies.
The liquid level height of the ink liquid in the reservoir tank moves upwards or downwards because of a balance between a supply amount of the ink liquid from the ink tank and a supply amount of the ink liquid into the plurality of ink heads. When the liquid level height of the ink liquid moves upwards or downwards, the inflow port of the overflow liquid pipe is sometimes immersed in the ink liquid. In this state, the ink liquid sometimes enters the overflow liquid pipe, and remains as such in the overflow liquid pipe.
In Jpn. Pat. Appln. KOKAI Publication No. 2000-309109, a technique has been described in which a main discharge pipe is opened to the atmosphere to thereby return the ink liquid which has gotten into the discharge pipe to a sub-tank.